Gas chromatograph moisture analyzer



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BECOME Q Q Aug. 2, 1966 v, M. DAVIDSON GAS CHROMATOGRAPH MOISTUREANALYZER Filed April 1s, 1964 M| HA L DAVlDSON B ATTORNEY United StatesPatent O 3,263,493 GAS CHROMATOGRAPH MOISTURE ANALYZER Van MichaelDavidson, Baton Rouge, La., assignor to Esso Research and EngineeringCompany, a corporation of Delaware Filed Apr. 13, 1964, Ser. No. 359,1184 Claims. (Cl. 73--53) This invention relates generally to chromatographsysstems and, more particularly, to the use of Ia combinedchromatograph-hygrometer system for moisture analysis of hydrocarbons.

The presence of water in small quantities in liquid or gaseoushydrocarbons is harmful to refinery processes and the control ofmoisture content is necessary to assure proper results. Heretofore, ithas generally not been possible without elaborate techniques todetermine moisture content on stream in a Water-sensitive process andthen only after considerable delay. Consequently, information relatingmoisture content -to processes has necessarily been disjointed orperhaps completely unconnected with the condition which had `caused thesystems moisture content.

In accordance with the .present invention it is now possible todetermine moisture content in extremely small traces required by anon-stream system in a manner that such information may be directlyrelated to a process very nearly concurrently with the proces-s stream.

More specifically, an on-stream sample is first admitted to the moistureanalyzer of the invention. Using a dry carrier gas, the sample iscarried to a vaporizer and therefrom to a chromatographic column. Thelatter is constructed to pass entirely the hydrocarbons in the sample,while absorbing and holding for a predetermined time all of the mositurein the sample. By appropriate means, the initial hydrocarbon portion orfraction passed from the chromatographic column is llushed or otherwiseremover, preferably by using dry carrier gas and after the completeremoval of the hydrocarbon fraction, the output of the chromatographiccolumn is routed to a hygrometer, for example, of the electrolytic type.The construction of the chromatographic 'column is such that after theaforementiond predetermined time, the moisture of the on-stream sampleabsorbed therein is gradually released (eluted) and the hygrometer,being maintained at constant temperature and volt-age, will vary itscurrent output, depending upon the degree of moisture sensed. Thehygrometer may be connected to a recorder which preferably will maintaina continuous graphic record of current variations sen-sed by thehygrometer which, therefore, constitute a measure 'of the moisturecontent of Ithe sample.

The following presents a specific embodiment of the invention and adescription thereof in accordance with the accompanying drawing, inwhich:

FIG. 1 illustrates schematically a gas chromatographhygrometer moistureanalyzer in accordance with the above-outlined principle of theinvention; and

FIGS. 2 and 3 represent details of alternate valve positions of FIG. 1.

Referring to the drawing, sample stream 1 is under the control o-f astream switching valve 2 which may be actuated to release a samplecomprising, for example, 2 milliliters of a hydrocarbon from a direct oron-stream portion of -a chemical process. The sample may be in a giveninstance, propylene or ethylene, at 100-200 p.s.i. The sample will firstbe trapped in the valve and sample loop as shown in the position ofvalve 2 of FIG. 1. Actuation 'of the valve to its alternate position ofFIG. 2 causes the sample lloop `to be connected into line 2a through thevalve 2. The sample will thus be carried by -a slug of dry nitrogencarrier gas from its source 3 (under a ICC pressure of perhaps 30 lbs.)toward and into an oven 4. Intermediate the carrier gas source 3 and thesample is a kickback restrictor 5 whose function ifs to prevent passageof the sample hydrocarbon beyond such restrictor, while permittingexpansion of the sample because of the disparity between the initialon-stream pressure of 200 p.s.i. of the sample and the 30 lbs. ofcarrier gas pressure.

Accordingly, the sample carried by the dry carrier gas is fed to avaporizer 6 in an oven 4 which is maintained at a constant temperatureof 200 F. The vaporizer prepares the sample containing both hydrocarbonand moisture for introduction into a chromatographic column 7 alsosituated in the oven 4.

As is known in the art of constructing chromatographic columns, theabsorption agent used in the column may be selected to absorb and retainfor a predetermined time the moisture in the sample while passingcompletely the hydrocarbon portion or fraction thereof. In the presentembodiment, wherein it is postulated that the hydrocarbon sample itselfmay consist of propylene or ethylene,-

the agent used in the chromatographic column may consist of polyethyleneglycol having a molecular weight of 750. Such agent having an efnity formoisture only will, therefore, absorb the latter and pass thehydrocarbon fraction.

The hydrocarbon fraction passing through the column will proceed withthe carrier gas to a valve 8 which, initially, via line 8a and throughvalve 8, will be connected to a vent. As a consequence, the initialhydrocarbon fraction of the test sample passed by the chromatographiccolumn will be flushed through the valve 8 and therefrom vented for aninitial period which may be in the order of 13- 14 minutes. During thistime, the column 7 will completely absorb al-l of the moisture contentof the test sample, in perhaps the first 3-4 minutes of the period withthe remainder acting to clear the column completely of the hydrocarbonfraction. It will be seen that a second portion of the dry carrier gasmay proceed from the source 3 through a variable restrictor 10 whichwill be set to feed carrier gas at approximately 100 ccs/min. to thevalve 8. When the latter is in the position of FIG. 1, dry gas willproceed through valve 8 via line 8b to a hygrometer 11 (to be described)in order to purge the hygrometer of any moisture therein.

After the initial period of 13-14 minutes, the valve will be switched toroute the output of the chromatographic column to the hygrometer 11.Hygrometer 11 will be a sensitive electrolytic hygrometer, for example,such as -a Beckman hygrometer, suitable to measure 1-1000 parts permillion of water in the test sample and presently manufactured by theBeckman Instrument Company of Fullerton, California. Briefly thehygrometer comprises a moisture detector wherein moisture released bythe chromatographic column, subsequent to separating out the hydrocarbonfraction of the sample, will be absorbed on phosphorous pentoxide(P205). After about 15 minutes from the beginning of passage of thesample through the column 7, the absorbed moisture therein will bereleased (eluted) to the hygrometer for detection therein.

The hygrometer has a control 12 which maintains the hygrometer atconstant temperature and volt-age. Current variations as an output fromthe hygrometer will result from the electrolytic breakdown of themoisture in the hygrometer cell. Such variations in the current outputof Ithe cell will be fed as indicated to la recorder 13, preferably of acontinuous graphic record variety whose trace, when calibrated,therefore represents moisture content of the sample sensed by thehygrometer. This information may then, of course, be related to thesample itself which is of known volume.

By the foregoing, it is now therefore possible to assure nearlycontinuous, on-stream monitoring of a refinery process and moisturepresence at selected critical points. The information is very closelyrelated in time to the actual operation of the process such that theeiect of moisture in the process land control of the process itself inaccordance therewith may be directly correlated.

It will be understood that the foregoing description relates merely to arepresentative embodiment and that, for example, various moisturedetectors other than the specic electrolytic hygrometer illustrated anddescribed may be used with similar results. Furthermore, other changesmay be made from the described particular embodiment without departingfrom the teachings of the invention. Accordingly, in order to appreciatethe true spirit and scope of the invention, .attention is directed tothe appended claims.

What is claimed is:

1. A gas chromatograph-hygrometer moisture analyzer for a hydrocarbonsample containing hydrocarbon and moisture portions comprisingchromatographic means for absorbing all moisture from said sampleproduct for a predetermined time While passing through saidchromatographic means the hydrocarbon portion thereof, `means forpassing said hydrocarbon portion sequentially and initially from saidchromatographic means, a hygrometer, and means for passing the moistureportion of said sample to said hygrometer subsequent to the eliminationof the hydrocarbon portion of said sample from said chromatographicmeans.

2. The analyzer of claim 1 in which there are means for removing saidsample from an on-stream portion of a process, a vaporizer, meanscomprising a dry carrier gas for passing said sample to said vaporizer,means for passing said sample from the vaporizer, a switching valve forreceiving the output of said chromatographic means and initiallypositioned to vent the hydrocarbon portion of said sample, said valvebeing constructed in combination with conduit means for passing saidmoisture portion to said hygrometer, and means connected to thehygrometer for recording the moisture content of said sample.

3. The analyzer of claim 2 in which said hygrometer is an electrolytictype hygrometer maintained -at constant voltage, wherein currentvariations therefrom cornprise a measurement of moisture content in saidsample and the current output of said hygrometer is connected to arecorder capable of continuously graphically recording said variationsof current.

4. The analyzer of claim 3 in which the chromatographic means comprisesa column having an absorption agent of polyethylene glycol having =amolecular weight in the order of 750, said vaporizer and column arelocated within an oven, and dry gas means is connected to said switchingvalve for flushing said hygrometer when lthe switching valve ispositioned to vent said hydrocarbon portion from the chromatographiccolumn.

References Cited bythe Examiner UNITED STATES PATENTS 2,934,693 4/1960Reinecke et al. 73-23.l X

LOUIS R. PRINCE, Primary Examiner.

1. A GAS CHROMATOGRAPH-HYGROMETER MOISTURE ANALYZER FOR A HYDROCARBONSAMPLE CONTAINING HYDROCARBON AND MOISTURE PORTIONS COMPRISINGCHROMATOGRAPHIC MEANS FOR ABSORBING ALL MOISTURE FROM SAID SAMPLEPRODUCT FOR A PREDETERMINED TIME WHILE PASSING THROUGH SAIDCHROMATOGRAPHIC MEANS THE HYDROCARBON PORTION THEREOF, MEANS FOR PASSINGSAID HYDROCARBON PORTION SEQUENTIALLY AND INITIALLY FROM SAIDCHROMATOGRAPHIC MEANS, A HYGROMETER, AND MEANS FOR PASSING THE MOISTUREPORTION OF SAID SAMPLE TO SAID HYGROMETER SUBSEQUENT TO THE ELIMINATIONOF THE HYDROCARBON PORTION OF SAID SAMPLE FROM SAID CHROMATOGRAPHICMEANS.